1. Field of the Invention
The present invention relates to a method of making a fiber suspension for use in a paper-making machine, and, more particularly, to a method of removing wax from recycled cellulosic fiber used to make such a fiber suspension.
2. Description of the Related Art
Petroleum waxes have long been used in the paper converting industry to provide cellulosic paper products moisture resistance and wet strength. These paper products include corrugated boxes, paper cups, waxed paper wrapper, and waxed roll-wrap laminates. Of these products, corrugated boxes account for the majority of wax consumed. When wax is applied to corrugated boxes, the main objective is to provide board structural integrity in humid and wet environments.
The majority of wax used with corrugated board is petroleum wax, a by-product of the automotive lubricating oil refining process. In this process, crude oil is distilled (separated by boiling) into various products such as gasoline, naptha, fuel oil, gas oil, and paraffin distillates. Paraffin wax is the solid component of the paraffinic distillate. Paraffin wax is a crystalline structured polymer composed primarily of a mixture of hydrocarbon molecules. Solid paraffin waxes are usually white, translucent, tasteless, and odorless. They are hard, relatively brittle, and have a slightly greasy feel. In a molten state, paraffin waxes are clear, colorless liquids of low viscosity. The melting point of paraffin waxes ranges from 43-71.degree. C. Blended wax is a combination of paraffin with or without other waxes usually in conjunction with non-wax additives such as resins, rosins, polymers, and copolymers.
There are currently three methods to apply wax to corrugated paperboard.
a) Impregnating
The material is dipped or submerged into a bath of molten wax. The paper board will pick up 10-20% of its weight in wax. The wax is usually a food grade paraffin of low viscosity. If only one component is treated, it is almost always the medium.
b) Saturating or Cascading
A thick "waterfall" of wax is flushed into or over the finished board, or the board is dipped in a bath of molten wax. The board will pick up 35-50% of its weight in wax. The wax is usually a simple, medium viscosity blend of fully refined paraffin and additive.
c) Curtain Coating
The material is passed horizontally through a thin curtain of falling wax. The board will pick up 5-7 lb of wax per thousand square feet of board. The wax is usually a complex blend of fully refined paraffin and several additives, resulting in a very high viscosity product.
Waxed old corrugated container (OCC), entering through the collection process, is the largest source of wax contamination in paper recycling mills. These waxes present a major obstacle to the paper recycling industry. The problems with wax for paper-making are as follows:
a) Presence of wax in a paper sheet results in the reduction of the coefficient of friction, which in turn causes troubles in rewinding, converting, and box stacking. PA1 b) Waxes tend to deposit on the surface of fibers, thus lowering the interfiber bonding strength. The paper and board made from such fibers possess lower strength properties when the amount of wax in the paper and board reaches 0.5% . Also, there is some loss in stiffness. PA1 c) Paper and board containing wax generally have poor printability and glueability. PA1 d) Non-dispersed waxes (such curtain coating) introduce unpleasant spots in paper sheets during drying. PA1 e) Occasionally waxes can aggravate a pitch problem. Wax tend soften the pitch, thus making it more tacky. PA1 f) Low-viscosity waxes (used for cascading or impregnating processes) are easily dispersed during pulping at elevated temperatures. The dispersed waxes are such fine particles that conventional mechanical separation equipment, such as screen and cleaner, are not effective in removing these contaminants. PA1 g) Wax removal by washing requires water clarification since wax is not removed from the liquid phase. Wax build-up in white water is not acceptable in paper mills. In addition, washing is not effective in removing large particle wax.
Because of the above-mentioned troubles with waxes, waxed OCC and other waxed paper products have been classified as non-recyclable. As such, waxed OCC is generally sorted out at the recycling plant and incinerated or land filled.
What is needed in the art is a method of removing wax from a fiber suspension made from waxed cellulosic fiber, such as waxed OCC.